Intraoperative and In Vitro Classification of Subacromial Bursal Tissue

Human Rotator Cuff Tears Reveal an Age-Dependent Increase in Markers of Cellular Senescence and Selective Removal of Senescent Cells With Dasatinib + Quercetin Increases Genetic Expression of COL1A1 In Vitro

PURPOSE

To quantify cellular senescence in supraspinatus tendon and subacromial bursa of humans with rotator cuff tears and to investigate the in vitro efficacy of the senolytic dasatinib + quercetin (D+Q) to eliminate senescent cells and alter tenogenic differentiation.

METHODS

Tissue was harvested from 41 patients (mean age, 62 years) undergoing arthroscopic rotator cuff repairs. In part 1 (n = 35), senescence was quantified using immunohistochemistry and gene expression for senescent cell markers (p16 and p21) and the senescence-associated secretory phenotype (SASP) (interleukin [IL] 6, IL-8, matrix metalloproteinase [MMP] 3, monocyte chemoattractant protein [MCP] 1). Senescence was compared between patients <60 and ≥60 years old. In part 2 (n = 6) , an in vitro model of rotator cuff tears was treated with D+Q or control. D+Q, a chemotherapeutic and plant flavanol, respectively, kill senescent cells. Gene expression analysis assessed the ability of D+Q to kill senescent cells and alter markers of tenogenic differentiation.

RESULTS

Part 1 revealed an age-dependent significant increase in the relative expression of p21, IL-6, and IL-8 in tendon and p21, p16, IL-6, IL-8, and MMP-3 in bursa (P < .05). A significant increase was seen in immunohistochemical staining of bursa p21 (P = .028). In part 2, D+Q significantly decreased expression of p21, IL-6, and IL-8 in tendon and p21 and IL-8 in bursa (P < .05). Enzyme-linked immunosorbent assay analysis showed decreased release of the SASP (IL-6, MMP-3, MCP-1; P = .002, P = .024, P < .001, respectively). Tendon (P = .022) and bursa (P = .027) treated with D+Q increased the expression of COL1A1.

CONCLUSIONS

While there was an age-dependent increase in markers of cellular senescence, this relationship was not consistently seen across all markers and tissues. Dasatinib + quercetin had moderate efficacy in decreasing senescence in these tissues and increasing COL1A1 expression.

CLINICAL RELEVANCE

This study reveals that cellular senescence may be a therapeutic target to alter the biological aging of rotator cuffs and identifies D+Q as a potential therapy.

The effect of augmenting suture material with magnesium and platelet-rich plasma on the in vitro adhesion and proliferation potential of subacromial bursa-derived progenitor cells

Background

Connective tissue subacromial bursa-derived progenitor cells (SBDCs) have been suggested as a potent biologic augment to promote healing of the repaired rotator cuff tendon. Maximizing the amount of retained progenitor cells at the tendon repair site is essential for ensuring an optimal healing environment, warranting a search for proadhesive and proliferative adjuvants. The purpose was to evaluate the effect of magnesium (Mg), platelet-rich plasma (PRP), and a combination of both adjuvants on the in vitro cellular adhesion and proliferation potential of SBDCs on suture material commonly used in rotator cuff surgery.

Methods

SBDCs were isolated from subacromial bursa samples harvested during rotator cuff repair and cultured in growth media. Commercially available collagen-coated nonabsorbable flat-braided suture was cut into 1-inch pieces, placed into 48-well culture dishes, and sterilized under ultraviolet light. Either a one-time dose of 5 mM sterile Mg, 0.2 mL of PRP, or a combination of both adjuvants was added, while a group without treatment served as a negative control. Cellular proliferation and adhesion assays on suture material were performed for each treatment condition.

Results

Augmenting the suture with Mg resulted in a significantly increased cellular adhesion (total number of attached cells) of SBDCs compared to PRP alone (31,527 ± 19,884 vs. 13,619 ± 8808; P < .001), no treatment (31,527 ± 19,884 vs. 21,643 ± 8194; P = .016), and combination of both adjuvants (31,527 ± 19,884 vs. 17,121 ± 11,935; P < .001). Further, augmentation with Mg achieved a significant increase in cellular proliferation (absorbance) of SBDCs on suture material when compared to the PRP (0.516 ± 0.207 vs. 0.424 ± 0.131; P = .001) and no treatment (0.516 ± 0.207 vs. 0.383 ± 0.094; P < .001) group. The combination of Mg and PRP showed a significantly higher proliferation potential compared to PRP alone (0.512 ± 0.194 vs. 0.424 ± 0.131; P = .001) and no treatment (0.512 ± 0.194 vs. 0.383 ± 0.094; P < .001). There were no significant differences in the remaining intergroup comparisons (P > .05, respectively).

Conclusion

Augmenting suture material with Mg resulted in a significantly increased cellular adhesion of SBDCs compared to untreated suture material, as well as augmentation with PRP alone or a combination of both adjuvants. Further, Mg with or without PRP augmentation achieved a significant increase in the cellular proliferation of SBDCs on suture material compared to untreated sutures and augmentation with PRP alone. Application of Mg may be a clinically feasible approach to optimizing the use of SBDCs as a biological augment in rotator cuff repair, while combined augmentation with PRP may harness the full potential for optimized tissue recovery due to the high concentration of PRP-derived growth factors.

Editorial Commentary: Rotator Cuff Repairs Fail at an Alarmingly High Rate During Long-Term Follow-Up: Graft Augmentation and Biologics May Improve Future Outcomes

Rotator cuff repairs (RCR) frequently fail to heal, particularly those with advanced fatty infiltration, supraspinatus and infraspinatus atrophy, narrowed acromiohumeral distance, and large-to-massive tear size. Unfortunately, the longer the follow up, the more sobering the statistics, with some reported retear rates ranging up to 94%. Importantly, recent long-term radiographic assessments after primary RCR reveal direct correlations between failure and patient-reported outcomes, functional deterioration, and ultimately, progression of glenohumeral arthritis and/or frank cuff tear arthropathy. As shoulder surgeons, we must continue to seek out novel approaches to improve tendon to bone healing and recapitulate the native rotator cuff enthesis. In doing so, we hope to engender more sustained subjective and objective results for our patients over time. Investigations are ongoing into several biomechanical and biological or structural adjuncts, from platelet-rich plasma and bone marrow aspirate concentrate to autograft or allograft structural augments. We must continue to push the envelope and refuse to settle for the current reality and alarmingly high failure rates following RCR.

Advances in Stem Cell Therapies for Rotator Cuff Injuries

Rotator cuff injury is a common upper extremity musculoskeletal disease that may lead to persistent pain and functional impairment. Despite the clinical outcomes of the surgical procedures being satisfactory, the repair of the rotator cuff remains problematic, such as through failure of healing, adhesion formation, and fatty infiltration. Stem cells have high proliferation, strong paracrine action, and multiple differentiation potential, which promote tendon remodeling and fibrocartilage formation and increase biomechanical strength. Additionally, stem cell-derived extracellular vesicles (EVs) can increase collagen synthesis and inhibit inflammation and adhesion formation by carrying regulatory proteins and microRNAs. Therefore, stem cell-based therapy is a promising therapeutic strategy that has great potential for rotator cuff healing. In this review, we summarize the advances of stem cells and stem cell-derived EVs in rotator cuff repair and highlight the underlying mechanism of stem cells and stem cell-derived EVs and biomaterial delivery systems. Future studies need to explore stem cell therapy in combination with cellular factors, gene therapy, and novel biomaterial delivery systems.

Subacromial Bursal Tissue and Surrounding Matrix of Patients Undergoing Rotator Cuff Repair Contains Progenitor Cells

PURPOSE

To build upon previous literature to identify a complete analysis of cellular contents of subacromial bursal tissue as well as the matrix surrounding the rotator cuff.

METHODS

Samples of subacromial bursal tissue and surrounding matrix milieu from above the rotator cuff tendon and above the rotator cuff muscle bellies were obtained from 10 patients undergoing arthroscopic rotator cuff repair. Samples were analyzed using fluorescent-activated cell sorting and histologic analysis with staining protocols (Oil Red O, Alcian Blue, and Picro-Sirius Red), for identification of matrix components, including fat, proteoglycans, and collagen.

RESULTS

Progenitor cells and fibroblast-type cells were present in significant amounts in subacromial bursal tissue in both tissues obtained from over the tendinous and muscle belly portions. Markers for neural tissue, myeloid cells, and megakaryocytes also were present to a lesser extent. There were prominent amounts of fat and proteoglycans present in the matrix, based on ImageJ analysis of stained histologic slides.

CONCLUSIONS

The subacromial bursal tissue and surrounding matrix of patients undergoing rotator cuff repair contains progenitor cells in significant concentrations both over the tendon and muscle belly of the rotator cuff.

CLINICAL RELEVANCE

This presence of progenitor cells, in particular, in the subacromial bursal tissue provides a potential basis for future applications of augmentation purposes in rotator cuff healing, and calls into question the practice of routine bursectomy. As the potential role of bursal tissue contents in growth and regeneration in the setting of rotator cuff healing is more well understood, maintaining this tissue may become more relevant. Concentration of these cellular components for use in autologous re-implantation is also an avenue of interest.

Trochanteric Bursa Is a Source of Connective Tissue Progenitor Cells

Purpose

To investigate the presence of connective tissue progenitor cells (CTPs) in the trochanteric bursa harvested over the gluteus medius muscle belly and tendon during open hip procedures.

Methods

Trochanteric bursa samples from nine patients (63.1 ± 8.6 years) undergoing total hip arthroplasty for primary osteoarthritis were obtained from 2 sites: over the gluteus medius tendon at the greater trochanter and over the muscle belly. Bursal tissue was digested with collagenase and grown in culture. The nucleated cell count, cellular concentration, cellular proliferation, fluorescence-activated cell sorting (FACS) analysis, and differentiation using immunostaining and quantitative polymerase chain reaction (PCR) were used to determine and quantify the presence of CTPs.

Results

Bursa-derived CTPs were identified in all harvested samples. At t = 0, there was no difference in nucleated cell count over muscle and tendon (1.69 ± 1.26 × 10⁸ and 1.41 ± 1.12 × 10⁸ cells/g, respectively; P = .162). Similarly, the cellular concentration at 3 weeks was not significantly different between bursa harvested over muscle and tendon (6.61 ± 5.14 × 10⁶ and 5.58 ± 4.70 × 10⁶ cells/g, respectively; P = .532). High cellular proliferation was identified for both bursal tissue overlying muscle and tendon (2.28 ± .95 and 1.66 ± 1.05, respectively; P = .194). FACS analysis revealed high positivity rates (>95%) of CTP-specific surface epitopes (CD105, CD90, and CD73) and low positivity rates (<1.3%) of negative markers (CD45, CD31). Osteogenic, adipogenic, and chondrogenic differentiation potential was demonstrated with immunostaining and quantitative PCR for gene expression.

Conclusions

Connective tissue progenitor cells are found in the trochanteric bursa overlying the muscle and tendon of the hip abductors.

Clinical Relevance

During open hip procedures, the trochanteric bursa is often partially excised to identify muscular boundaries and tissue planes for surgical exposure. The function of the trochanteric bursa remains largely unknown. However, this tissue is a source of connective tissue progenitor cells, which may be important in the healing response of surgically repaired abductor tendons.

Histological and molecular features of the subacromial bursa of rotator cuff tears compared to non-tendon defects: a pilot study

Background

The role of the subacromial bursa in the development or healing of shoulder pathologies is unclear. Due to this limited knowledge, we aimed to understand specific reactions of the subacromial bursa according to rotator cuff (RC) pathologies compared to non-tendon defects of the shoulder. We hypothesized that the tissue composition and inflammatory status of the bursa are likely to vary between shoulder pathologies depending on the presence and the extent of RC lesion.

Method

Bursa samples from patients with either 1) shoulder instability with intact RC (healthy bursa, control), 2) osteochondral pathology with intact RC, 3) partial supraspinatus (SSP) tendon tear, or 4) full-thickness SSP tear were investigated histologically and on gene expression level.

Result

Bursae from SSP tears differed from non-tendon pathologies by exhibiting increased chondral metaplasia and TGFβ1 expression. MMP1 was not expressed in healthy bursa controls, but strongly increased with full-thickness SSP tears. Additionally, the expression of the inflammatory mediators IL1β, IL6, and COX2 increased with the extent of SSP tear as shown by correlation analysis. In contrast, increased angiogenesis and nerve fibers as well as significantly upregulated IL6 and COX2 expression were features of bursae from patients with osteochondral pathology. Using immunohistochemistry, CD45+ leukocytes were observed in all examined groups, which were identified in particular as CD68+ monocytes/macrophages.

Conclusion

In summary, besides the strong increase in MMP1 expression with SSP tear, molecular changes were minor between the investigated groups. However, expression of pro-inflammatory cytokines correlated with the severity of the SSP tear. Most pronounced tissue alterations occurred for the osteochondral pathology and full-thickness SSP tear group, which demonstrates that the bursal reaction is not exclusively dependent on the occurrence of an SSP tear rather than longstanding degenerative changes. The present bursa characterization contributes to the understanding of specific tissue alterations related to RC tears or non-tendon shoulder pathologies. This pilot study provides the basis for future studies elucidating the role of the subacromial bursa in the development or healing of shoulder pathologies.

Analysis of Patient Factors Affecting In Vitro Characteristics of Subacromial Bursal Connective Tissue Progenitor Cells during Rotator Cuff Repair

Unsatisfactory failure rates following rotator cuff (RC) repair have led orthopaedic surgeons to explore biological augmentation of the healing enthesis. The subacromial bursa (SB) contains abundant connective tissue progenitor cells (CTPs) that may aid in this process. The purpose of the study was to investigate the influence of patient demographics and tear characteristics on the number of colony-forming units (CFUs) and nucleated cell count (NCC) of SB-derived CTPs. In this study, we harvested SB tissue over the supraspinatus tendon and muscle in 19 patients during arthroscopic RC repair. NCC of each sample was analyzed on the day of the procedure. After 14 days, CFUs were evaluated under a microscope. Spearman’s rank correlation coefficient was then used to determine the relationship between CFUs or NCC and patient demographics or tear characteristics. The study found no significant correlation between patient demographics and the number of CFUs or NCC of CTPs derived from the SB (p > 0.05). The study did significantly observe that increased tear size was negatively correlated with the number of CFUs (p < 0.05). These results indicated that increased tear size, but not patient demographics, may influence the viability of CTPs and should be considered when augmenting RCrepairs with SB.

Decreased Colony-Forming Ability of Subacromial Bursa-Derived Cells During Revision Arthroscopic Rotator Cuff Repair

Purpose

To compare the cellular viability and differentiation potential of subacromial bursa-derived cells (SBDCs) located over the rotator cuff muscle and tendon of patients undergoing primary versus revision arthroscopic rotator cuff repair (ARCR).

Methods

Subacromial bursa was harvested from 18 primary (57.1 ± 4.6 years) and 12 revision ARCRs (57.3 ± 6.7 years). Bursa was collected from 2 sites (over rotator cuff tendon and muscle), digested with collagenase, and grown in culture. The number of nucleated cells, colony-forming units (CFUs), differentiation potential, and mesenchymal stem cell surface markers were compared in primary and revision cases.

Results

There was no difference in the number of nucleated cells between primary and revision ARCR harvested from the subacromial bursa overlying the tendon (3019.3 ± 1420.6 cells/mg and 3541.7 ± 2244.2 cells/mg, respectively; P = .912) or muscle (2753.5 ± 1547.1 cells/mg and 2989.0 ± 2231.4 cells/mg, respectively; P = .777). There was no difference in the number of CFUs between primary and revision ARCR over the rotator cuff tendon (81.5 ± 49.5 CFUs and 53.0 ± 36.9 CFUs, respectively; P = .138), but there were significantly fewer CFUs over the muscle in revision cases (28.1 ± 22.7 CFUs) compared with primary cases (55.7 ± 34.5 CFUs) (P = .031). SBDCs from revision ARCR expressed characteristic mesenchymal stem cell surface epitopes and had multidifferentiation potentials for chondrogenesis, osteogenesis, and adipogenesis.

Conclusions

SBDCs harvested over the rotator cuff muscle demonstrated significantly decreased colony-forming abilities in revision arthroscopic rotator cuff repairs compared with primary repairs. However, the subacromial bursa retains its pluripotent differentiation potential for chondrogenic, osteogenic, and adipogenic lineages in the revision setting.

Clinical Relevance

The subacromial bursa may play a role in the healing response of the repaired rotator cuff. This capacity is not necessarily diminished in the revision setting and may be harnessed as an orthobiologic.

Arthroscopic Rotator Cuff Repair Augmented with Autologous Subacromial Bursa Tissue, Concentrated Bone Marrow Aspirate, Platelet-Rich Plasma, Platelet-Poor Plasma, and Bovine Thrombin

As recurrent rotator cuff tears following repair remain a significant problem, improving healing potential using biologic adjuvants, including concentrated bone marrow aspirate (cBMA), platelet-rich plasma (PRP), or subacromial bursa tissue (SBT), has become increasingly popular in recent years. In an attempt to combine the benefits of these various biologic adjuvants and maximize the healing potential of the repaired tendon, an arthroscopic rotator cuff repair technique biologically augmented with autologous SBT, cBMA, PRP, platelet-poor plasma (PPP), and bovine thrombin has been developed. The created clot is used as a biologic scaffold for sufficient delivery, and it is stabilized using bovine thrombin in order to ensure maximum stability and retainment of the applied biologic augments at the repair site.

CLASSIFICATIONS

I: shoulder; II: rotator cuff.

The Effect of Insulin and Insulin-like Growth Factor 1 (IGF-1) on Cellular Proliferation and Migration of Human Subacromial Bursa Tissue

Purpose

To evaluate the effect of a one-time dose of insulin or insulin-like growth factor 1 (IGF-1) on cellular proliferation and migration of subacromial bursa tissue (SBT) over time.

Methods

SBT was harvested from over the rotator cuff tendon in 4 consecutive patients undergoing primary arthroscopic rotator cuff repair. SBT was cultured for 3 weeks in complete media until reaching confluence. The culture dishes were stored in a humidified, low oxygen tension (5% CO₂) incubator at 37°C. SBT of each patient underwent treatment with a one-time dose of insulin or IGF-1, whereas nontreated SBT served as a negative control. Cellular proliferation and migration were evaluated after 24, 48, 72, and 96 hours of incubation. SBT-derived cells migrated in the detection field were visualized using fluorescent microscopy.

Results

Cellular proliferation at 24, 48, 72, and 96 hours was 1.40 ± 0.27, 1.00 ± 0.20, 1.47 ± 0.31, and 1.68 ± 0.28 for IGF-1; 1.44 ± 0.24, 1.15 ± 0.27, 1.60 ± 0.36, and 1.61 ± 0.32 for insulin; and 1.51 ± 0.35, 1.29 ± 0.33, 1.53 ± 0.35, and 1.57 ± 0.38 for nontreated SBT. Untreated SBT demonstrated a significantly greater proliferation when compared with IGF-1 and insulin within the first 48 hours, although this effect was found to subside by 96 hours. Cellular migration at 24, 48, 72, and 96 hours was 575.7 ± 45.0, 641.6 ± 77.7, 728.3 ± 122.9, and 752.3 ± 114.5 for IGF-1; 528.4 ± 31.3, 592.5 ± 69.8, 664.2 ± 115.2, and 695.6 ± 148.2 for insulin; and 524.4 ± 41.9, 564.4 ± 49.8, 653.2 ± 81.5, and 685.7 ± 115.5 for nontreated SBT. Insulin showed no difference in migration at each timepoint compared to nontreated SBT (P > .05, respectively).

Conclusions

Insulin and IGF-1 initially inhibit cellular proliferation of human SBT, although this effect was found to subside by 96 hours. Further, neither insulin nor IGF-1 changed the slope of cellular migration over time. However, each treatment group demonstrated a significant increase in cellular proliferation and migration.

Clinical Relevance

In the setting of biologic augmentation of rotator cuff repair, the compatibility and synergistic effect of insulin on human SBT is highly limited.

Preliminary Clinical Outcomes Following Biologic Augmentation of Arthroscopic Rotator Cuff Repair Using Subacromial Bursa, Concentrated Bone Marrow Aspirate, and Platelet-Rich Plasma

Purpose

To evaluate the clinical outcomes of patients who underwent arthroscopic rotator cuff repair augmented using subacromial bursa, concentrated bone marrow aspirate (cBMA), and platelet-rich plasma.

Methods

Sixteen patients were included in the study who underwent arthroscopic rotator cuff repair augmented using subacromial bursa, cBMA, and platelet-rich plasma from January 2018 to July 2018 and had a minimum 1-year follow-up. American Shoulder and Elbow Surgeons (ASES), Simple Shoulder Test, Constant-Murley, and Single Assessment Numerical Evaluation (SANE) scores were collected preoperatively and at terminal follow-up. To determine the clinical relevance of ASES scores, the minimal clinically important difference, substantial clinical benefit, and the patient acceptable symptomatic state thresholds were used. In vitro cellular proliferation of subacromial bursa (nucleated cells/gram) and cBMA (nucleated cells and colony-forming units/cc) samples was evaluated and correlated to clinical outcomes scores.

Results

Mean follow-up was 12.6 ± 1.8 months (range 12-19 months). Patients achieved significant improvement in ASES (45.8±22.5_pre vs 88.5 ± 14.6_post, Δ44.7 ± 20.7; P = .001), Simple Shoulder Test (4.3 ± 3.2_pre vs 10.4 ± 1.6_post, Δ5.7 ± 3.9, P = .002), Constant-Murley (44.3 ± 18.2_pre vs 83.6 ± 17.5_post, Δ37.2 ± 21.8; P = .001), SANE (13.3 ± 10.7_pre vs 86.3 ± 17.5_post, Δ71.9 ± 22.9; P = .001), and pain scores (5.0±2.8_pre vs 1.1 ± 1.6_post, Δ3.5±2.5, P = .001) at final follow-up. With regards to ASES score, 93.8% of patients achieved the minimal clinically important difference, 93.8% the substantial clinical benefit, and 62.5% reached or exceeded the patient acceptable symptomatic state criteria. There was a significant positive correlation of nucleated cell count of cBMA with postoperative SANE score (r = 0.707; P = .015) and delta in ASES score (r = 0.727; P = .011). All other correlations were found to be nonsignificant (P > .05, respectively).

Conclusions

Patients undergoing arthroscopic rotator cuff repair augmented using the Mega-Clot with bursa technique achieved significant improvement in functional outcomes at a minimum 1-year follow-up, with 93.8% of patients reaching substantial clinical benefit.

Level of Evidence

Level IV, therapeutic case series.

Editorial Commentary: Mesenchymal Stem Cells in the Shoulder Subacromial Bursa: Do Cells Understand Statistical Significance?

Local, arthroscopic harvest of mesenchymal stem cells is of interest due to their potential to augment healing. The high rates of retear after rotator cuff repair are a significant concern, and solutions, such as augmentation with mesenchymal stem cells, are being sought. The subacromial bursa of the shoulder is a potential source of cells to augment healing.